Touch panels or touch screen panels are a particular class of electronic visual display, which are able to detect and locate a touch within a display area. Generally, touch panels include a layer stack and are configured to sense a touch. The body of a touch panel should substantially be transparent, so that light in the visible spectrum emitted by the screen can be transmitted therethrough. At least some known touch panels include a transparent conductor formed over a substrate. A touch on the display area of such a panel generally results in a measurable change of capacitance in a region of the conductor. The change in capacitance may be measured using different technologies, so that the position of the touch can be determined.
A layer stack including a conductive layer for use with a touch panel is subject to some particular requirements. In particular, one key requirement is that the layer stack is stable enough for withstanding multiple contacts on the screen and harsh conditions, so that reliability of the touch screen is not compromised over time. However, at least some known layer stacks included in touch screens, which are considered robust, interfere with a proper transmission of light therethrough due to, for example, thickness, composition, and structure of the conductive layers. Furthermore, fabricating such a stable layer stack with high quality, for example with a uniform and defect-free barrier, is challenging.
Further, particular consideration of the optical characteristics, e.g. the appearance to a user, has to be taken into account for layer stacks, especially when the conductive layer for measuring the change in capacitance is a structured conductive layer. Thereby, a design of thin film based flat panel displays and touch screen technologies, which provides an invisible object, which is patterned with respect to conductivity (like a touch sensor structure) and which exhibits enhanced optical and electrical performance compared to conventional structures, is desired.
In view of the above, it is an object of the present invention to provide a layer stack for a touch panel, a touch panel and a method for forming a layer stack for a touch panel that overcomes at least some of the problems in the art and provides the desired properties.